Vacuum-ultraviolet photolysis of N2H2: Generation of NH fragments

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Abstract
The photodissociation of the double bond in HN=NH yielding electronically excited NH(A 3Π) and ground state NH(X 3Σ−) radicals has been studied in the vacuum‐ultraviolet above 105 nm. Fragment excitation spectra were taken using tunable synchrotron radiation as the photolysis light source. The excited radicals were detected by their triplet emission to the ground state. A very crude estimate results in 10%, 20%, and 70% of the excess energy to be channeled into fragment vibration, rotation, and translation, respectively, at the Kr resonance line at 123.6 nm. This energy distribution supports a repulsive process with almost equal rotation in the two NH fragments and vibration caused by lengthening all bonds during the N=N bond breaking. An upper limit for the energy necessary to break the double bond is measured to be 510.7±1.2 kJ mol−1. This value yields ΔfH00(N2H2)≥204.1±2.2 kJ mol−1.